1. Field of the Invention
The present invention is broadly concerned with improved agriculturally useful, quick drying coating compositions and methods wherein the compositions include one or more polycarboxylated polymer salt and a volatile organic drying agent. More particularly, the invention is concerned with such compositions and methods wherein a copolymer containing respective quantities of maleic and itaconic moieties is supplemented with a volatile drying agent, which may be mixed with or coated onto solids, such as solid nitrogenous fertilizer. In another aspect of the invention, improved drying times are provided by adding boron, especially in conjunction with vinylic polymer(s) having a majority of pendent functional groups thereof as alcohols, and optionally containing both relatively low and high molecular weight (MW) polymer fractions, to the copolymer-organic drying agent compositions.
2. Description of the Prior Art
U.S. Pat. No. 6,515,090 describes a highly useful class of copolymers which have been employed to good effect in a number of agricultural applications. For example, the '090 patent discloses copolymers made up of varying percentages of maleic and itaconic moieties, and salts thereof, which can be applied to solid fertilizers to achieve surprising increases in yields. In normal practice, an aqueous copolymer mixture is applied by spraying or other means onto solid fertilizers to provide fertilizer-polymer compositions.
Specialty fertilizer products, LLC of Leawood, Kans., commercializes a series of copolymers under the '090 patent. One such polymer, Nutrisphere-N® for granular nitrogen fertilizers, is especially designed to be applied to a variety of solid or granular nitrogen fertilizers, such as urea, ammonium salts, MAP, or DAP. This product is an approximately 40% by weight solids aqueous dispersion of a 1:1 partial calcium salt copolymer of maleic and itaconic moieties having a pH of from about 3.25-3.75.
However, it has been found that, depending principally upon the moisture content of the solid fertilizer, suboptimal field application procedures, or adverse ambient conditions such as very high humidity or low temperatures, problems with successful application of the above-mentioned compositions can arise. Specifically, the compositions are sprayed or otherwise deposited on the outer surfaces of solid fertilizers and the water is allowed to evaporate by mass transfer, leaving a solid polymer residue coating. However, if the composition drying time is excessive resulting in incomplete drying of the compositions, the coated products can be difficult to handle and apply. Indeed, in certain cases, relatively wet solid fertilizers with applied aqueous copolymer can create agglomerations within field application equipment making it difficult or even impossible to evenly spread the compositions across fields.
Mixtures of certain polycarboxylated polymers and organic solvents are known, see U.S. Pat. No. 5,868,964, e.g., polyacrylic acid polymer plus methanol. However, owing to the type of polymer used, and/or the concentration of organic solvent, the polymer and solvent are essentially incompatible, resulting in viscous precipitates unsuitable for use in fertilizer compositions. Polycarboxylate polymer salts do not usually form stable solutions in the presence of significant concentrations of organic solvents such as methanol.
There is accordingly a need in the art for improved agricultural products such as solid fertilizers in contact with quick-drying polycarboxylated polymers, so as to alleviate polymer coating and drying problems, while at the same time not detracting from the yield benefits obtained using such polymers.